This invention relates to a method for protecting underwater surfaces, in particular metal surfaces, against pollution due to fouling.
It is known that surfaces which generally or regularly are situated under water, in particular, parts of the hulls of ships and such, are rapidly polluted due to fouling by organisms present in the water, such as algae or other beings living in water, such as, for example, crustaceae.
Such pollution by biological growth on the hull of a ship below the water level increases the weight of the ship and increases the friction in the water, as a result of which the energy consumption for navigating is increased.
Cleaning these surfaces is time-consuming and expensive.
Therefore, attempts are made to prevent the pollution due to fouling, and to this aim a coating, a so-called anti-fouling coating, is applied to the surface.
This coating may consist of one or more layers of paint to which a chemical biocide has been added.
These biocides, however, gradually are released into the water and are very harmful for the water fauna and flora. In most cases, they are also aggressive in respect to the metal of the ship""s hull.
Moreover, such layers of paint regularly have to be renewed, which has to be performed in a dry dock and is relatively expensive.
WO-A-94/19415 discloses such anti-fouling coating comprising copper oxide. Copper ions, which are toxic to aquatic and marine organisms, are released in the water
Other known coatings consist of one or more layers of a synthetic material, for example, polyester, to which glass flakes are possibly added for reinforcement.
Although by the coating consisting of synthetic material the pollution is strongly reduced, this pollution, anyhow, still takes place rather fast.
The invention aims at a method for protecting underwater surfaces against pollution due to fouling which offers a better protection than the aforementioned known methods.
According to the invention, this aim is achieved in that an under-water surface upon which a coating wherein glass particles, so-called xe2x80x9cglass flakesxe2x80x9d are provided, has been applied, is protected by brushing or polishing smooth the coating, before or after fouling, in the presence of water, with at least one brush having bristles made of synthetic material into which a grinding agent is embedded.
This method utilizes the observation that, the smoother the surface, the slower the pollution due to fouling under water is taking place. By brushing or polishing, a very smooth surface can be obtained.
The brushing or polishing may take place under water or aground, however, in this last case during brushing or polishing, water has to be provided on the brushed surface.
U.S. Pat. No. 5,915,436 discloses a brush having bristles made out of polymer containing abrasive particles. No specific use is mentioned.
DE-A-2.016.575 discloses a device for removing fouling from underwater bodies, said device comprising rotating brushes. The brushes may be steel wire brushes, but in one embodiment these steel wire brushes are replaced by brush-like elements to which grinding means are bonded.
According to the invention, preferably, the brushing or polishing is performed by means of a brush with bristles in which aluminium oxide or silicium carbide particles are embedded.
The bristles of the brush can be manufactured of a supple synthetic material, such as nylon, polyethylene, polyester and similar.
An additional protection against pollution due to fouling then can be obtained by brushing or polishing a coating in which glass flakes-are provided to which a non-toxic agent against micro-organisms is bonded.
It was noted that the micro-pollution is strongly counteracted by means of the agent against micro-organisms.
The coating can be provided in at least two layers, whereby at least in the outermost layer these glass flakes, with a non-toxic agent against micro-organisms bonded thereto, are applied.